Reduction of the amplitude of higher order harmonic frequencies in pulsed electrical signals

Reduction of RF emissions is very crucial for better EMI performance in electrical equipment, for instance installed in automobiles. In this thesis, a flexible curve shaping module for a dcto- dc PWM converter is developed to achieve efficient reduction of RF emission. The design of the curve shaping module employs a programmable logic circuit (CPLD) where a lookup table is stored with a certain reference curve shape. A D/A converter converts the digital signal from the CPLD to analogue signal which is then fed to power stage to reproduce the reference curve shape on the output. This output signal can be fed to electrical load. The aim with the module is to employ different lookup tables corresponding to different curve shapes resulting in flexibility of the circuit. Frequency response for different curve shapes i.e. trapezoidal, sinusoidal and low pass filter response were studied in theory for comparing their EMI performance. These curves are also implemented in the real circuit for checking the response from the power stage. By evaluating the practical circuit, it was found out that RF emissions were lowered compared to hard switching techniques. Moreover various curve shapes were followed with sufficient accuracy on the output of the power stage with resistive load. When inductive loading is attached to the output of the power stage, the circuit enhances problems associated with controllability